Sometimes a simple solution is a better solution.
Over the past couple of years, I have identified over 5,600 phrases, patterns, and keywords commonly used by spammers and comment bots in usernames, email addresses, link text, and URIs. This blacklist is still a work in progress and there is certainly room for optimization. Suggestions are always appreciated.
Copy the list of keywords, paste it into the Comment Blacklist field of your WordPress Discussion Settings panel, and click the “Save Changes” button.